1. Field
The present disclosure relates generally to communication systems, and more particularly, to a transmit diversity architecture with optimized power consumption and an area for Universal Mobile Telecommunications (UMTS) and Long Term Evolution (LTE) systems.
2. Background
Wireless communication systems are widely deployed to provide various types of communication content such as voice, data, and so on. These systems may be multiple-access systems capable of supporting communications with multiple users by sharing the available system resources (e.g., bandwidth and transmit power). Examples of such multiple-access systems include code division multiple access (CDMA) systems, time division multiple access (TDMA) systems, frequency division multiple access (FDMA), 3GPP Long Term Evolution (LTE) systems, and orthogonal frequency division multiple access (OFDMA) systems, and Universal Mobile Telecommunications (UMTS) systems.
Generally, a wireless multiple-access communication system can simultaneously support communication for multiple wireless terminals. Each terminal communicates with one or more base stations via transmissions on the forward and reverse links. The forward link (or downlink) refers to the communication link from the base stations to the terminals, and the reverse link (or uplink) refers to the communication link from the terminals to the base stations. This communication link may be established via a single-in-single-out, multiple-in-single-out or a multiple-in-multiple-out (MIMO) system.
A MIMO system employs multiple (NT) transmit antennas and multiple (NR) receive antennas for data transmission. A MIMO channel formed by the NT transmit and NR receive antennas may be decomposed into NS independent channels, where NS—≧min {NT, NR}. Each of the NS independent channels corresponds to a dimension. The MIMO system can provide improved performance (e.g., higher throughput and/or greater reliability) if the additional dimensionalities created by the multiple transmit and receive antennas are utilized. When multiple transmit antennas are used, the system can also be described as having transmit diversity.
A MIMO system may support time division duplex (TDD) and/or frequency division duplex (FDD) systems. In a TDD system, the forward and reverse link transmissions can be on the same frequency region so that the reciprocity principle allows the estimation of the forward link channel from the reverse link channel. This enables the base station to extract transmit beamforming gain on the forward link when the multiple antennas are available at the base station. In an FDD system, forward and reverse link transmissions are on different frequency regions.
Modern cellular phones support multiple carriers and modes of operation. Increasingly, mobile devices are using MIMO systems to provide improved wireless communication performance. While mobile devices often utilize the latest advances in technology, there remains a need to provide legacy services. Frequently, a mobile device must be capable of transmit diversity while still operating in a legacy mode when necessary. Providing such capabilities often requires an increase in silicon area to provide the added features and modes of operation.
In the past, multiple transmit chains for MIMO or transmit diversity for cellular communications may have been implemented using multiple transmit chips. However, this is an inefficient use of silicon area and power and requires duplicate synthesizers for the two transmit chips. Duplicate transmit chains could have been implemented on the same chip, thus saving a synthesizer, but this causes the chip area to grow dramatically, which makes the chip unsuitable for products which only support the legacy mode, and causes high power consumption in the MIMO or transmitter diversity mode. There is a need in the art for a system architecture that provides for transmit diversity and optimized power consumption and is also suitable for use with UMTS and LTE systems. In addition, there is a need in the art for a space saving on the chip, and a need for a reduced size transmit chain.